即使我可以挂载由其制成的DMG，我也无法挂载VHD文件，并且file似乎认为vhdd和.dmg文件是同一种文件文件。我在使用VirtualBox 6.0.12r133076的macOS 10.14.6上。
这是我要执行的操作的记录（以错误结尾）：
$ hdiutil create -megabytes 2 -fs ExFAT foo.dmg
created: /Users/matt/tmp/foo.dmg
$ vboxmanage convertfromraw --format vhd foo.dmg foo.vhd
Converting from raw image file="foo.dmg" to file="foo.vhd"...
Creating dynamic image with size 2097152 bytes (2MB)...
$ mkdir foo_mnt
$ vboximg-mount --image=$(pwd)/foo.vhd foo_mnt
$ file foo.dmg
foo.dmg: DOS/MBR boot sector; partition 1 : ID=0x7, start-CHS (0x3ff,254,63), end-CHS (0x3ff,254,63), startsector 1, 4095 sectors, extended partition table (last)
$ file foo_mnt/vhdd
foo_mnt/vhdd: DOS/MBR boot sector; partition 1 : ID=0x7, start-CHS (0x3ff,254,63), end-CHS (0x3ff,254,63), startsector 1, 4095 sectors, extended partition table (last)
$ hdiutil attach foo.dmg
/dev/disk3 FDisk_partition_scheme
/dev/disk3s1 Windows_NTFS /Volumes/Untitled 1
$ hdiutil attach foo_mnt/vhdd
hdiutil: attach failed - image not recognized
更新：真的只是文件扩展名吗？如果我做ln -s foo_mnt/vhdd something.dmg，则可以使用
$ hdiutil attach something.dmg